Add version 3.1.0 to CHANGELOG

Author: magjac

CHANGELOG.md

@@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [3.1.0]
+
 ### Added
 * New option *useSharedWorker* that enables the use of a [shared web worker](https://developer.mozilla.org/en-US/docs/Web/API/SharedWorker). The default is still to use a [dedicated web worker](https://developer.mozilla.org/en-US/docs/Web/API/Worker).
 * New method [*graphviz*.**destroy**()](README.md#graphviz_destroy) to remove the Graphviz render from the element it was created on and release any resources it is holding.
@@ -70,7 +72,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## 2.x & 1.x
 See the [release notes](https://github.com/magjac/d3-graphviz/releases).
 
-[Unreleased]: https://github.com/magjac/d3-graphviz/compare/v3.0.6...HEAD
+[Unreleased]: https://github.com/magjac/d3-graphviz/compare/v3.1.0...HEAD
+[3.1.0]: https://github.com/magjac/d3-graphviz/compare/v3.0.6...v3.1.0
 [3.0.6]: https://github.com/magjac/d3-graphviz/compare/v3.0.5...v3.0.6
 [3.0.5]: https://github.com/magjac/d3-graphviz/compare/v3.0.4...v3.0.5
 [3.0.4]: https://github.com/magjac/d3-graphviz/compare/v3.0.3...v3.0.4